If you can afford the HVX get it- but that’s a pretty big jump in price vs. the DVX100B. With the B you get a lot of nice refinements but IMHO if your DVX100 serves you well now it’s not enough to upgrade. I’ve had mine for a few years and will probably go to the HVX when the time is right.
On what sort of material? Motion bogs down no matter what once you get to high def stuff or lots of layers, especially with particle effects. 8-9 FPS is not the worst I’ve heard.
That’s an optical side effect. I would not suggest trying to overcompensate with digital sharpenening and skin detail as you’ll be adding noise and artifacting. Nonetheless a properly calibrated production monitor will be critical to shooting.
I suggest keeping things pretty close to zero on most settings. If you correct too far in any one direction your hands will be tied in post. Also depends more on what the final output is. For example, vdetail thick should be used for TV projects while thin should be used for projects destined for eventually output to film.
You can get a pretty good setting by pressing auto iris and then switching back to manual. Also carrying a good production monitor. There’s also a spot meter setting.